The overall objective is to characterize the DMBA-induced hyperplastic lesions of the rat mammary gland and to examine their neoplastic potential. One major approach is to compare several transplantable outgrowth lines of hyperplastic lesions with regard to stability, morphology, growth patterns, tumor producing potential, and hormone-dependence and responsiveness. The second major approach involves the use of the mammary hyperplasias by DMBA. This latter approach should facilitate analysis of the interactions of carcinogen, hormones, and isolated mammary target tissue and may elucidate mechanisms and control of cell transformation.